Confirmed cases of anthrax in the United States have sparked panic across the world - and a spate of bogus threats. Why do hoaxers send suspects packages?

A package arrives, or perhaps an envelope, from an unknown sender. Inside is a white powder.

Those at risk have been given antibiotics

The building is cleared, the police called in, the suspicious substance taken away for testing. It turns out to be harmless - but the fear and uncertainty caused are anything but.

Hoaxers have fanned such fears the world over. Suspect packages have turned up as far afield as Mexico, Malaysia and South Africa in the wake of the outbreak in the United States.

In the UK, the government has acted to try to stop the spate of anthrax hoaxes. From Sunday, anyone found to be behind a chemical, nuclear or biological hoax now faces up to seven years in jail.

The scares distract from real emergencies

Psychologist Paul Mathias, a recently retired detective superintendent with the Metropolitan Police, says hoaxers often need to feel powerful and in control.

"They like to feel that they can control the lives of others, that they can communicate but can't be identified.

"Often they may do it for their own sense of self-esteem. They are keen to identify themselves as somebody who controls lives, which is something they can't do in their everyday lives."

Get 'them' back

With extensive coverage of the events of 11 September and fears of further terror attacks, some may feel that they want to play a part in pushing events along.

The Liverpool scare turned out to be a false alarm

"The same thing happened with the IRA troubles," Mr Mathias says. "A number of hoaxers have been unable to offer any explanation other than they thought something should be happening."

Others may make bogus threats for attention, for revenge for some perceived slight, or even for a laugh, says Gerard Bails, a consultant forensic psychologist.

And in some cases, those sending suspect packages will be sympathetic to the terror attackers' cause, Mr Bails says.

"This is an extremely effective terrorism technique because it causes disruption and chaos. It's a way of causing fear without actually fighting your enemy, without putting yourself in danger."

False alarms the world over

In uncertain times, even the slightest perceived threat can cause panic.

Removing a suspect package in Brazil

On Friday, experts warned that the fear of biological attacks may cause more illness than the weapons themselves. In a letter to the British Medical Journal, researchers in the UK, US, and Australia said fear and anxiety could remain high for years.

Already, there are reports of mass "sociogenic" illness. On 29 September, for instance, paint fumes set off a bioterrorism scare at a school in Washington State, sending 16 students and a teacher to the hospital.

The anthrax outbreaks in the US heightened fears

Mr Mathias puts this in part down to our herd mentality.

"At workplaces where some people respond with extreme anxiety, others who might not normally react like that will feel they have to exhibit the same concerns."

Yet for many, the attacks on New York and Washington punctured their sense of safety in the world and left them unsure how to react.